If shoes are needed... shoe on time! Trim according to growth. The inability for the hoof to wear naturally (because there is steel in the way) in between farrier appointments makes it important to do it fairly often. Why? If the hoof cannot wear... the toe tends to get long... longer than what would ever happen barefoot on an exfoliating type of terrain. The break over during movement now causes torque or stress on the hoof that encourages hoofwall stretching/separation.
Although a horse may appear to be sound, this occurring perpetually over years can actually change the internal structures, snowballing into a self preservation mode of altered foot fall and landing, which then snowballs into a plethora of pathology such as under-run heels, varied navicular changes, toe separation, diseased frogs and sulcus area cracks, cysts on the bone... the list goes on.